The invention relates to a method for the autostereoscopic representation of images on a display screen having a pixel grid, wherein a parallax separating optical plate composed of a plurality of segments is disposed in front of the screen, and image information for left and right eyes of at least one user is displayed in interleaved pixel patterns on the screen, the method comprising the steps of:
a) applying an algorithm for allocating the total of the image information to be displayed at a time to at least two textures such that each texture includes the information for one view; and
b) for each pixel, applying a sampling algorithm for sampling image information from selected areas of the textures for determining an image content of the pixel, wherein, when a pixel is correlated with more than one texture, the sampling algorithm comprises a step of determining a correlation factor of the pixel with each of said textures and a step of blending sampling results from each of said textures in accordance with the corresponding correlation factors.
In an autostereoscopic display, a three-dimensional visual impression is achieved by presenting slightly different views to the left and the right eye of a viewer, such that the difference in the two views corresponds to the parallactic displacement of near objects relative to a more distant background. To create these different views a ‘parallax separating optical plate’ is employed which assures that different views are visible for the left and the right eye of the user. The optical plate is composed of a plurality of segments and may for example be a lens array, where the segments are lenses and the effect is used that for any given point of view, some of the pixels on the screen are magnified, while other pixels remain invisible. The positions of visible and invisible pixels on the screen will depend upon the configuration of the lens array and the positions of the eyes of the user, so that it is possible to display the image information on the screen in such a way that for a given view position one eye of the viewer will only see the pixels belonging to one view, whereas the other eye will only perceive the pixels that belong to the other view. As an alternative, the parallax separating optical plate may be formed by a barrier mask wherein the segments form a pattern of transparent and non-transparent parts, or by an equivalent optical system.
In a typical embodiment the lens array is composed of cylindrical lenses with an inclination relative to the direction of the columns of the pixel grid in order to avoid moiré and to obtain a well balanced image with respect to the unavoidable loss of optical resolution.
U.S. Pat. No. 6,801,243 B1 discloses a so-called multi-view system. The term “multi-view” indicates that the number N of views is larger than 2. Still, the views will include at least one view for the left eye and at least one view for the right eye, and these two views constitute a so-called stereo-pair. However, there may be a plurality of stereo-pairs, which will become visible one after the other when the user moves his head sideways relative to the screen. The image contents of the different stereo-pairs may be selected so that they reflect not only the parallactic displacement but also an apparent rotation of the three-dimensional objects resulting from the change in the aspect angle under which the objects are viewed, so that the user, when moving his head, will have the impression that he actually “moves around” the 3D objects.
US 2013/057575 A1 discloses a multi-view system which permits to change the number of views.
In conventional multi-view systems, a relative abrupt, perceptible transition occurs when the viewer changes his position from one stereo-pair to a neighbouring one. These transitions can be smoothened by increasing the number N of different views. However, the increased number of views comes at the cost of reduced resolution, because in an N-view system maximally 1/N of the number of pixels in a pixel line of the screen will be visible at a time to a particular eye.
In the known systems, the number N of views is determined by a well-defined relation between the lens array and the pixel grid of the screen so that an integer number of pixels is assigned to each lens and each pixel holds content of one of the N views. The lenses of the lens array and the pixel lines of the screen may be considered to constitute a coarse pixel grid composed of “super pixels” having a height corresponding to one or more screen pixel lines and a width corresponding to the width of an individual lens. For each of the N views, each super pixel must include at least one screen pixel that is assigned to that view. It is possible, however, that the number of screen pixels per super pixel is a non-integral number.
WO 2008/011888 A1 (EP 2 044 480 B1) discloses a system according to the preamble of claim 1. This system is a two-view system (N=2), wherein, however, the number of screen pixels per view and lens and pixel line is larger than 2. In order to allow for changes of the viewing position, this system may be equipped with an eye tracker, i.e. a camera and suitable software for determining the actual view position of a user, and the assignment of the screen pixels to the left or right channel, i.e. to the view for the left eye or the right eye of the viewer, is changed dynamically in accordance with the detected view position. In each super pixel, the screen pixels that are not visible from the given view position are used for displaying duplicates of the visible image information which generates a certain amount of redundancy, such that a greater robustness is achieved when the user moves his head and an eye tracking system is either not available or is not quite fast enough to follow-up in real time. Furthermore this configuration allows to adapt the system to different viewing distances.
The system disclosed in EP 2 044 480 B1 is particularly adapted to take advantage of the enhanced capabilities of modern graphics cards for driving the display screen, in particular the capability to operate on specific data structures that are termed “texture maps” or in short “textures”. A texture is a two-dimensional array which contains image information stored in “texels” (similar to a conventional bitmap which contains “pixels”) and these texels are mapped to pixels on the screen. The image content displayed in a pixel on the screen with the position (x, y) is a function of the two texture coordinates (u, v) which designate the position of this image information in the texture. The convention is that 0≤u≤1 and 0≤v≤1 so that u and v are non-integral values which do not refer to individual texels. In addition to the (u, v) coordinates a sampling method must be specified. Sampling methods can be standard (like ‘bicubic sampling’) or customized, and their complexity can range from simple to very elaborate. The choice of the suitable sampling method depends on a number of aspects and almost always involves a trade-off, with the intended image quality and the capabilities of the hardware being the two most important aspects.
Textures provide an advantageous way of storing image information. However, unless otherwise noted, in the context of this invention the term ‘texture’ shall be used in a more general way for any structure that contains image information of a certain view.
The image information for the two different views that are available in this system is stored in two different textures. Each screen pixel is assigned to either of the two views which are displayed through two channels. In the first place, the assigned channel decides from which texture the data are to be sampled. However, when a pixel is located at a boundary between two channels (e.g. the pixel is assigned to the left channel, but its immediate neighbour is assigned already to the right channel), the system offers the possibility to determine the image content of the pixel by blending information from the two textures in a way so that this blend reflects the location of the boundary with maximum accuracy. In certain types of 2-view autostereoscopic displays these ‘border’ pixels are normally invisible to both eyes. They may however become visible at least temporarily when the user moves his head sideways or changes the viewing distance from the screen. In these cases, the feature of blending information improves the image quality and makes the system more robust.